Soil function reshaping and crop yield driving mechanisms in saline-alkali soil under freezing saline water irrigation

Introduction: Freshwater scarcity and soil salinization constrain agricultural production in arid and semi-arid regions. Freezing saline water irrigation (FSWI) offers a potential strategy for using saline water during the freeze-thaw period, but the optimal irrigation amount and its yield-driving mechanisms remain unclear. Methods: Here, a three-year field experiment was conducted from 2022 to 2024 in Dalad Banner, Inner Mongolia, China, with four FSWI treatments of 0, 90, 180 and 270 mm. We evaluated pre-sowing soil hydrothermal, salinity and microbial functional indicators, and assessed sunflower growth, yield and seed quality under uniform agronomic management. Results: Among the treatments, FSWI180 showed the best overall performance. It maintained favorable pre-sowing soil moisture and salinity conditions, increased yield by 93% relative to the non-irrigated control, and improved seed oil content to 43.96%. It also achieved the highest comprehensive growth and quality indices, with mean GI and QI values of 2.126 and 1.182, respectively. XGBoost-SHAP analysis identified soil moisture, total salinity, electrical conductivity and community robustness as the main yield-driving factors, together accounting for 74.75% of the total contribution. Discussion: These results indicate that 180 mm FSWI can coordinate soil water storage, salinity regulation and microbial functional stability, thereby supporting stable yield improvement and high-quality sunflower production in cold arid saline-alkali regions.